1. Field of the Invention
This invention relates generally to semiconductor devices and techniques for their manufacture, and more particularly, to semiconductor devices and manufacturing techniques for encapsulating interconnect structure that has been fabricated of copper.
2. Discussion of the Related Art
Typically, in the manufacture of high-density semiconductor devices, multiple layers of conductive material connected by vias or plugs are provided above a substrate. Such multiple layers, typically of metal, are employed in order to accommodate high device densities. While aluminum has been used mainly in the past for metallization within integrated circuits, as metal lines are scaled down to smaller dimensions (including decreasing widths), the problem of failure due to electromigration, which may lead to open or shorted metal lines, has become significant. Additionally, as dimensions of metal lines further decrease, metal line resistance increases, and this increase may adversely affect circuit performance.
Presently, the use of copper in interconnect structure is receiving great attention, because copper has lower bulk resistivity than aluminum and potentially higher electromigration tolerance than aluminum.
With damascene dimensions of conductors decreasing below 0.1 micron in width or diameter, the aspect ratio of a copper interconnect may well exceed 5:1. In such a situation, when forming a copper interconnect by electroplating, a highly conformal and low-resistivity base layer is needed prior to such formation. A currently used ion metal plasma (IP) base layer contains both a high resistivity barrier layer (for example Ta or TaN) and a copper seed layer with relatively high resistance (due to the effect of increased thin-film resistance with decreasing thickness), leading to circuit performance problems as discussed above. Furthermore, such a base later has low conformality and extendability when applied to small features, so that voids are readily formed in high aspect ratio trench/vias.
Therefore, what is needed is a method for providing high conformality of a base layer in a copper electroplating process, meanwhile providing for high conductivity and high electromigration resistance of the copper metallization.